0741-3106 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LED.2015.2416689, IEEE Electron Device Letters > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—A spin based analog-to-digital converter (ADC) using magnetic tunnel junctions (MTJs) is proposed in this report. Our proposal is based on a novel high-speed low-power MTJ comparator that is controlled through spin Hall (SHE) and voltage-controlled magnetic anisotropy (VCMA) effects. According to the simulation results, spin ADC offers features including high sampling rate, low-power consumption, and less chip area occupation for higher bit resolution while provides the benefit of non-volatility of conversion results. Index Terms—Analog-to-Digital Converter (ADC), Magnetic Tunnel Junction, Spin Hall Effect, Voltage Controlled Magnetic Anisotropy I. INTRODUCTION nalog-to-digital converter (ADC) acts as a bridge between analog and digital worlds, which can translate physical quantities e.g., light, sound, temperature or pressure to digital numbers that can be processed by computer. The recent predictions of ADC trends based on a near-exhaustive survey of reported scientific ADC performance show no obvious improvement on resolution and power consumption in next 10 years assuming using the current architecture and operation mode [1,2,3]. To fulfil requirements of communication industries and sensor technologies, such as ultra-wideband (UWB) and software defined radios (SDRs), performance of ADCs in terms of bandwidth, sampling rate (Fs), resolution rate and power consumption should be consistently improve through adopting new technologies or novel device design. The semiconductor industry is progressively going toward “hybrid CMOS” integrated circuits and particularly trying to integrate non-volatile memories to reduce static power consumption and increase the bandwidth. For the non-volatile circuit design, magnetic tunnel junction (MTJ) is one of the promising candidates due to its high retention time, long endurance, and CMOS compatible process technology. With the further development of MTJ technology, it can play an important role in future integrated circuits (ICs), not only limited to memory units, but also for logic units and sensors [4,5]. In this letter, a spintronic ADC concept is introduced for the Manuscript received Jan 27, 2015. This work was supported partially by National Science Foundation (NSF) Nanoelectronics Beyond 2020 program under Award Number NSF-NEB (1124831) and C-SPIN, one of six STARnet program Centers. Yanfeng Jiang, Yang Lv, Mahdi Jamali, Jian-Ping Wang are with the University of Minnesota, Minneapolis, MN 55455 USA (Corresponding author with phone 1-612-625-9509; e-mail: jpwang@umn.edu). first time utilizing magnetic tunnel junctions (MTJs) as its main elements. Spin Hall effect (SHE) and voltage-controlled magnetic anisotropy (VCMA) are utilized to control the MTJ elements and convert the analog to digital signal. Design and simulation of spin comparator II. DESIGN AND SIMULATION OF MTJ COMPARATOR High-speed and low power comparators are essential building blocks in high-speed ADC. Conventional comparator consists of several stages of amplifiers and latches[1,2]. Fig.1(a) presents the proposed MTJ comparator, which consists of one spin Hall driven MTJ device and one transistor. Its cross-sectional schematic is given in Fig.1(b). Two switching mechanisms are included in the device operation such as spin Hall effect (SHE) and voltage controlled magnetic anisotropy (VCMA). Fig.1 (a) SHE-MTJ based comparator, including one SHE-MTJ and one transistor. The effect of voltage-controlled magnetic anisotropy is included in MTJ device. (b) Cross-sectional schematic of SHE-MTJ based comparator. Spin torque switching of MTJ using SHE has been demonstrated in a three-terminal device[6,7].The spin Hall device used to construct comparator, is composed of MTJ and spin Hall metal (SHM). The free layer of MTJ is in direct contact with SHM. If a charge current flows in the SHM, spin current can be generated transversely, thus exerting spin-transfer torque on the free layer for switching. Owing to the high spin injection efficiency combined with the low SHM resistance[6], switching energy could be very low. Wang et al. demonstrated the effect of VCMA on MTJ by measuring coercivities[8]. The effect originates from spin-dependent screening of the electric field which leads to notable changes in the surface magnetization and the surface magnetocrystalline anisotropy [9]. A voltage bias across a MTJ can modify the perpendicular anisotropy of the free layer. MTJ based comparator in Fig.1 integrates the spin Hall current and the VCMA together to implement its functions. The equivalent circuit is shown in Fig.2. The critical switching current IC0 dependson the demagnetizing field in perpendicular Spin Analog-to-Digital Convertor Using Magnetic Tunnel Junction and Spin Hall Effect Yanfeng Jiang, Yang Lv, Mahdi Jamali, Jian-Ping Wang, Fellow, IEEE A